In oil and gas wells, uncontrolled downhole fluid pressures can cause a dangerous situation. Depending on the downhole conditions, it is usually possible to predetermine a threshold pressure differential between a higher fluid pressure in an area exterior of the downhole tubing string adjacent where a safety-valve is to be positioned, and a lower fluid pressure interior of the tubing string that is considered to present an undesirable or possibly dangerous situation. For example, excessive fluid pressure in a production zone that is unbalanced by fluid pressure interior of the tubing string adjacent the production zone may present a highly dangerous situation in which hydrocarbons and gases may be driven at uncontrolled pressures uphole through the tubing string. In extreme cases, this can result in a blow-out of the well. A safety valve is intended to automatically actuate when such a condition occurs.
Another situation where this type of tool is valuable is if a leak develops in the tubing string above the valve that allows fluid pressure to communicate into the annular, where annulus pressure is harder to control. In this situation, it would be advantageous to have a valve that would automatically shut in the well.
It would be advantageous to have a safety valve that could be re-opened in response to a sufficient increase in interior fluid pressure over the exterior fluid pressure, whereby the downhole fluids can be pumped through the safety valve back into the formation.
It would also be advantageous to have a safety valve that would open a circulating valve after closing the fluid flow through the safety valve, whereby fluid can be circulated between the tubing string and the annulus while the flow through the safety valve is closed.
To operate successfully in the harsh and remove downhole environments, a simple and reliable safety valve structure and method would be highly advantageous.